The combinatorial approach to materials development depends on being able to rapidly synthesize sample libraries spanning diverse ranges of compositions and processing conditions. The approach has seen widespread application in the pharmaceutical and other sectors, but has been applied only tentatively in alloy development, largely because of the difficulties of rapidly synthesizing, under clean conditions and at high temperatures, series or libraries of samples large and homogeneous enough to exhibit bulk-like alloy properties.
Separately, the high cost of shaped alloy components made using conventional metallurgical processes has spurred development of a range of additive-manufacturing technologies, in which components are formed by sequentially depositing controlled amounts of material on selected areas of a work-piece surface while a localized heat source is applied to those areas. In such additive manufacturing technologies, the localized heat source is typically a laser, a directed plasma arc or an electron beam, and the material is typically fed in the form of a powder stream or wire.
Additive manufacturing systems that combine a localized heat source with one or more powder streams have been developed. For example, U.S. Pat. No. 5,961,862 (University of California) discloses an integrated deposition head delivering two or more gas-assisted powder streams having the same composition towards the focal region of the laser. However, the difficulty of incorporating even a substantial fraction of the incident powder stream (or streams) directed towards a small heated region, such as a pool of molten material produced by a focused laser, renders powder-based systems inherently unsuitable for use in combinatorial alloy development, which requires precise and accurate control of sample composition, and also increases the cost of components made by powder-based additive manufacturing.
Unlike powder feeders, a suitably configured wire-feeder can deliver substantially all of a length of wire, comprising an element or alloy, into a small region of molten material. Various wire feeders, allowing accurate and precise control of feed rate, rapid starting and stopping of the feed, and accurate and precise positioning of the end of a single wire, have been developed, generally for use in welding. US Pub. App. No. 2010/0089890 (Manning) describes a hand-held wire-feeder with a positioning tube for the relatively fine wires, 0.13 to 0.32 mm diameter, used in laser welding of jewelry, and U.S. Pat. No. 5,137,223 (US Dept. of Energy), a machine-controlled wire feeder, comprising a torque motor that applies tension to the wire and a stepper motor that advances an elastic-coated drive wheel to deliver wire through a hypodermic needle into the less than 0.25 mm diameter melt pools typical in high density electron beam or laser welding. A laser welding system having a separate wire-feeder for introducing wire into the output of a laser head integrated with a powder feeder, allowing switching between laser and powder feed, has also be proposed. US Pub. App. No. 2006/0049153 (Honeywell Int'l, Ltd.).
In order to improve process controllability and access to non-planar work-pieces, feed-heads having laser optical systems adapted to accommodate a single, axially-fed wire have been developed. U.S. Pat. No. 6,294,754 (Mitsubishi Heavy Indus., Ltd.); WO Pub. App. No. 2009/039753 (Suzhou Univ.). A plasma-arc feed-head comprising a single, axially-fed, wire has also been developed. U.S. Pat. No. 6,365,867 (Sandia Corp.). Such single-wire feed-heads are not capable of the rapid synthesis of combinatorial alloy sample series or libraries from multiple wires having diverse compositions.
U.S. Pat. No. 5,578,227 (Rabinovitch) discloses a rapid prototyping system comprising a wire feeder and delivery tube configured to pivot around the optic axis of a laser head, FIGS. 1; 5:55-6:6 & 6:9-14. U.S. Pat. No. 5,578,227, and proposes that composite prototype articles, comprising, for example, layers of stainless steel and an organic material, might be produced by alternating two wire feeders delivering two different materials. 7:3-9. U.S. Pat. No. 5,578,227 does not disclose combining the output of two wire feeders in a single molten region, either sequentially or simultaneously.
The present invention overcomes the above and other limitations of the prior art by employing an integrated multi-wire feed-head to form alloy samples having defined compositions, suitable for combinatorial alloy discovery and additive manufacturing applications.